Endothelial preservation in canine autogenous vein grafts prevents platelet and neutrophil adhesion, however, monocytes localize in the subendothelium and the endothelial number rises early after implantation. It is postulated in the present study that fragmentation of exposed subendothelial fibronectin (Fn) triggers monocyte infiltration and that subendothelial monocyte-derived macrophages play a protective role in promoting endothelial proliferation. The specific aims are to determine whether: 1) chemotactic monocytes in grafts are immunoreactive (ir) for intact Fn and for specific Fn fragments generated by controlled proteolysis, 2) monocyte transformation into macrophages precedes the onset of endothelial proliferation, 3) macrophages, endothelial cells, and extracellular matrix (ECM) are immunoreactive for basic fibroblast growth factor (bFGF), 4) endothelial replication is suppressed during monocytopenia induced by dexamethasone (Dex), and 5) bFGF concentrations are elevated in endothelial cells and ECM of grafts containing subendothelial macrophages. At early implantation periods, grafts will be retrieved to quantitate monocyte adhesion using antibody against surface antigen Mo2 and to evaluate the presence of Fn on monocytes using antihuman Fn antibody. Fragments or Fn with defined binding domains and molecular weights will be used to evaluate chemotaxis of canine monocytes in-vitro. Antibody to the chemotactic fragment will be produced in rabbits and used to immunohistochemically evaluate the presence of fragments on monocytes adherent to grafts. The number of monocytes (presence of peroxidase-positive granules and fluoride-inhibited nonspecific esterase activity) and transformed macrophages (presence of mannose receptors and fluoride-resistant nonspecific esterase activity) will be quantitated and examined in relation to endothelial thymidine labeling index. Polyclonal antibody to the synthetic replicate (Tyr 24 )bFGF(1-23) will be labeled with Ultragold secondary antibody and used to map and quantitate endothelial cell, macrophage, and ECM ir-bFGF by scanning transmission electron microscopy coupled with energy dispersive X-ray analysis and particle detection software. At sequential periods, the number of adherent monocytes, presence of ir-bFGF, and the endothelial thymidine labeling index of grafts in :he presence and absence of Dex will be compared by analysis of variance. The concentration of bFGF in graft endothelial cells and ECM will be compared to native vein artery. These studies may help to define whether the interaction between monocytes and endothelial cells is a protective mechanism evoked in vein grafts following implantation.